Phosphate rock flotation

ABSTRACT

A process for beneficiating phosphate rock containing siliceous and carbonaceous gangue materials and gypsum which comprises the steps of subjecting comminuted phosphate rock to a first stage anionic flotation step to float phosphates from siliceous material, conditioning the float product in an aqueous solution containing added phosphate ion and sulphate ion, subjecting the conditioned float product to a second stage anionic flotation step and recovering a concentrate product of high phosphatebearing mineral content.

United States Patent 1191 Johnston [451 Apr. 30, 1974 PHOSPHATE ROCK FLOTATION [75] Inventor: David Lawrence Johnston,

Yellowknife, Canada [73] Assignee: Cominco Ltd., Montreal, Quebec,

Canada 3,113,838 12/1963 Perri 209/166 X 3,405,802 10/1968 Prellen 209/166 3,462,016 8/1969 Bushell 209/166 3,462,017 8/1969 Bushell 209/166 Primary Examiner-Robert Halper 57 ABSTRACT A process for beneficiating phosphate rock containing siliceous and carbonaceous gangue materials and gypsum which comprises the steps of subjecting comminuted phosphate rock to a first Stage anionic flotation step to float phosphates from siliceous material, conditioning the float product in an aqueous solution containing added phosphate ion and sulphate ion, subjecting the conditioned float product to a second stage anionic flotation step and recovering a concentrate product of high phosphate-bearing mineral content.

5 Claims, 1 Drawing Figure 52 us. or. 209/166 [51 Int. Cl ..B03d l/02 [5 8] Field of Search 209/ 166 [56] References Cited UNITED STATES PATENTS 1,914,695 6/1933 Langeu 207/166 2,553,905 5/1951 Evans 209/166X 2,303,931 12/1942 Greene... ..209/166 2,698,088 12/1954 Pryor 209/166 10 W 8 O 8 e e 2 O 1 1 Q a R 6 5 2 0 .J 8 4- Z 6- SOLUBLE SULPHATE ADDITION mgpl PATENTEDAPR 30 m4 o m i s zoEjom SOLUBLE SULPHATE ADDITION mgpl INVENTOR. DAVID L.JOHNSTON PHOSPHATE ROCK FLOTATION BACKGROUND OF THE INVENTION This invention relates to a process for beneficiating phosphate bearing materials and is particularly directed to a flotation process for the concentration of phosphate minerals in phosphate rock high in silica, calcium carbonate, magnesium carbonate and gypsum.

U.S. Pat. Nos. 3,462,016 and 3,462,017 describe processes for the beneficiation of phosphate-bearingmaterials high in silica and in carbonates such as calcium carbonate and magnesium carbonate. The former patent teaches a two-stage anionic flotation process in which the bulk of the silica is removed as an underflow and the phosphate minerals and carbonates are removed as float in the first stage, and the phosphate minerals selectively depressed for removal as an underflow concentrate and the calcium and magnesium carbonates floated in the second stage; the float from the first stage being conditioned by the addition of phosphoric acid for depression of the phosphate minerals in the second stage. The latter patent teaches a two-stage anionic process wherein the phosphate minerals are selectively depressed prior to the second stage flotation by the addition of a soluble alkali phosphate to the flotation circuit.

SUMMARY OF THE INVENTION Although the processes taught in the aforesaid patents are effective for the beneficiation of phosphatebearing materials high in silica and in carbonates, it has been found that undesirable phosphate losses occur from the flotation solutions in the presence of gypsum. I have found surprisingly that the presence of a sulphate ion such as produced by a soluble sulphate salt, added in addition to the alkali phosphate or phosphoric acid in the conditioning step, results in a substantial reduction in the loss of soluble phosphate with significant economies in the operation of the process in that the cost of the sulphate salt consumed is considerably less than that of the additional phosphate recovered.

It is a principal object of the present invention therefore to provide an improved process for the beneficiation of phosphate-bearing materials containing gypsum for the recovery of phosphate minerals with minimum phosphate losses.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT As described in the above-noted patents, theiH PO{ ions provided through the addition of phosphoric acid or alkali phosphate in the conditioning step effectively deactivate the residual anionic collector on the surfaces of the phosphate particles whilenot affecting the activated surfaces of the calcium carbonate and magnesium carbonate particles. Thus, in the succeeding second stage anionic flotation an improved separation of calcium carbonate and magnesium carbonate from the phosphate minerals is achieved.

Although it will be understood that I am not bound by hypothetical considerations, it is believed that any gypsum contained in the ore causes a loss of soluble phosphate from t-hesolution through reaction of orthophosphate ions with gypsum for precipitation of .a brushite (CAHPO 2H O) surface layer or coating on the gypsum. A sufficient quantity of soluble phosphate must of necessity be added in the conditioning step,

therefore, over andabove that which becomes precipitated out by gypsum, in order to effectively accomplish the de-activation of the anionic collector on the surfaces ofthe phosphate particles. By means .of the present process, the loss of soluble phosphate, such'as ammonium phosphate, from the solution can be avoided or greatly reduced. This is of economic significance to the process for the phosphate make-up requirements are reduced to quantities necessary to compensate for physical lossesonly. The actual quantity saved will vary with the gypsum content of the first stage concentrate and may range from 5 to 20 lbs/ton equivalent of the final concentrate. Furthermore, it has been found that the presence of sulphate ions in the pulp does not adversely affect the flotation results.

The explanation in simple terms for loss of soluble phosphate because of the gypsum in ore is found in the equation:

This reaction can be hindered or prevented by adding soluble sulphates.

Another important reaction taking place in the system'is:

which, in conjunction with reaction (1) being held to the left in'the presence of an adequate concentration of sulphate ions, can lead to a release of phosphate from the ore to solution; It may be seen then that an'optimum addition of soluble sulphate'to the process is of some importance, for an excess addition will result in minor losses to solution of the phosphate it is being attempted-to recover from the ore.

l have found that, of the major mineral components v present in the phosphate flotation system, gypsum is the only mineral to remove significant'quantities of orthophosphate ions from solutionand the presence of from about} to about 6g/l, preferably about 4 g/l, of Na SO or the presence offrom about 2 to about 6-g/l, preferably about 3 g/l (NH,) SO effectively suppresses thereaction between gypsum and orthophosphate ions, as shown in the FIGURE.

The concentration of orthophosphate ion necessary to .depress apatite in the flotation'of ores, could be decreased by supplying sulphate ion toreduce I-IPOf ion loss through CaHPO .2I-I O formation. The sulphates useful in the two-stage reflotation process must have the effect of increasing the concentration of sulphate ion in the solutions and the only useful sulphates are those soluble sulphates which are in a salt form such as sodium, potassium and ammonium sulphates. Sulphuric acid is not satisfactory for this purpose in that the materials on which the two-stage anionic processes are practiced contain calcite and dolomite and the well-known reaction of sulphuric acid with calcite and dolomite produces the undesirable reaction products of gypsum, magnesium sulphate and carbon dioxide. The reactions are rapid and will continue as long as sulphuric acid is added or calcite and dolomite remain. The effect of adding sulphuric acid thus does not include raising the sulphate ion concentration in solution above the gypsum saturation level and sulphuric acid would therefore complicate the gypsum exchange of sulphate for soluble phosphate by introducing more gypsum.

The following example shows the effectiveness of the addition of a soluble sulphate salt to the conditioning step in the process of treating collophane phosphate rock of the type treated according to the processes of the above noted patents. A first stage flotation concentrate was prepared and aliquots of. this concentration, containing 0.1 percent sulphate sulphur corresponding to about 0.5 percent gypsum content, were treated by phosphate pulp reflotation for removal of calcite and dolomite, as described in the aforesaid patents. The following amounts of soluble sulphate were added to the flotation solution which contained 10 g/l NHI H PO Sulphate Amount Remarks T651 1 Nil Standard P loss 2 Na SO 3 gpl Reduced loss of P 0, 3 Na SO i5 gpl Gain of P 0 4 l0 gpl Gain of P 0,,

Losses of soluble phosphate were determined by measuring and assaying all filtrates and wash waters, with the following results:

Test ll l.8 lb/ton P 0 loss from solution Test 2 l .l lb/ton P 0 loss from solution Test 32.0 lb/ton P 0 gain to solution Test 4--4.6 lb/ton P 0 gain to solution It will be evident from the foregoing test results illustrated graphically in the FIGURE that, for a gypsum content of at least 0.5 percent in the first stage concentrate, the optimum sulphate addition would be from about 3 to about 6 g/l, preferably about 4 'g/l, for Na SO and would be about 2 to about 6 g/l, preferably about 3 g/l, for (NH SO What we claim as new and desire to protect by letters patent of the United States is:

l. in a process for beneficiating phosphate rock containing siliceous and carbonaceous gangue materials and gypsum in which soluble phosphates are lost by association with the gypsum and which includes the steps of subjecting comminuted phosphate rock to a first stage anionic flotation step for depressing siliceous ma terial, conditioning the float product in an aqueous solution containing added phosphate ion, subjecting the conditioned float product to a second stage anionic flotation step and recovering a concentrate product of high phosphate-bearing mineral content, the improvement which comprises adding a soluble sulphate salt selected from the group consisting of sodium sulphate and ammonium sulphate to the aqueous solution in said conditioning step whereby the losses of phosphates are reduced.

2. In a process as claimed in claim 1, adding from about 3 to about 6 g/l of Na SO to the aqueous solution in the conditioning step.

3. in a process as claimed in claim 1, adding about 4 g/l of Na SO to the aqueous solution in the conditioning step.

4. In a process as claimed in claim 1, adding from about 2 to about 6 g/l of (NH SO to the aqueous solution in the conditioning step.

5. In a process as claimed in claim 1, adding about 3 g/l of (NH SO to the aqueous solution in the conditioning step. 

2. In a process as claimed in claim 1, adding from about 3 to about 6 g/l of Na2SO4 to the aqueous solution in the conditioning step.
 3. In a process as claimed in claim 1, adding about 4 g/l of Na2SO4 to the aqueous solution in the conditioning step.
 4. In a process as claimed in claim 1, adding from about 2 to about 6 g/l of (NH4)2SO4 to the aqueous solution in the conditioning step.
 5. In a process as claimed in claim 1, adding about 3 g/l of (NH4)2SO4 to the aqueous solution in the conditioning step. 